Low Pressure Mercury Vapor Fluorescent Lamps

ABSTRACT

A low mercury consumption electric lamp is provided having a layer of a luminescent material comprising a phosphor derived from a mixture of a mixture of a cool-white calcium halophosphate, a red-emitting yttrium oxide (YOX), a green-emitting cerium, terbium lanthanum phosphate (LAP), and a blue-emitting europium-activated barium magnesium hexa-aluminate (BAM).

This application is related to U.S. application Ser. No. 10/259,713filed Sep. 27, 2002 of Gary Sigai et al., “Low Pressure Mercury VaporFluorescent Lamps”, commonly assigned herewith, the disclosure of whichis incorporated by reference.

This invention relates to low-pressure mercury vapor fluorescent lamps.

Low pressure mercury vapor lamps, more commonly known as fluorescentlamps, have a lamp envelope with a filling of mercury and rare gas tomaintain a gas discharge during operation. The radiation emitted by thegas discharge is mostly in the ultraviolet (UV) region of the spectrum,with only a small portion in the visible spectrum. The inner surface ofthe lamp envelope has a luminescent coating, often a blend of phosphors,which emits visible light when impinged by the ultraviolet radiation.

There is an increase in the use of fluorescent lamps because of reducedconsumption of electricity. To further reduce electricity consumption,there is a drive to increase efficiency of fluorescent lamps, referredto as luminous efficacy which is a measure of the useful light output inrelation to the energy input to the lamp, in lumens per watt (LPW).

Thus, more efficient and longer life fluorescent lamps are desired.However, a significant excess of mercury is introduced into the lamp tomeet desired long lamp lifetime of up to 20,000 hours or more. This isnecessary because different lamp components, such as the glass envelope,phosphor coatings and electrodes use up the mercury in the lamp. Suchincreased use of mercury is not desirable and is detrimental to theenvironment. Accordingly, there is a drive to reduce mercury consumptionin fluorescent lamps without a reduction in the lamp life.

An example of a successful lamp with reduced mercury consumption is theAlto cool-white Econowatt fluorescent lamp. These lamps usesmall-particle cool-white calcium halophosphate phosphor having anaverage particle size of about 8 to 12 microns and are doped with lessmercury than other lamps to meet the requirement of the ToxicCharacteristics Leaching Procedure (TCLP) of the United StatesEnvironmental Protection Agency for non-hazardous waste. To continue tomeet the rated life of these lamps, it is essential that the lamp andits components have low mercury consumption.

Similarly, fluorescent lamps of Daylight/Daylight Deluxe color have useda large-particle blue-halo calcium halophosphate phosphor as part of atwo-component blend that uses a standard white phosphor or a warm-whitephosphor as the other component. These lamps are doped with less mercuryto meet the TCLP requirement for non-hazardous waste. In U.S.application Ser. No. 10/259,713 referred to above, fluorescent lamps aredisclosed having a cool-white color with reduced mercury consumption inwhich a calcium-yellow calcium halophosphate phosphor is used in amixture of phosphors comprising about 41% of the calcium-yellow calciumhalophosphate phosphor. Such phosphor blends result in lamps having:reduced mercury content that pass the TCLP standards, excellentlong-life characteristics, etc. However, the phosphor blends from whichthe lamps are produced are dependent on the presence of calcium yellowhalophosphate as a component, and calcium yellow halophosphate is notreadily available commercially. There is therefore a continued need forfluorescent lamps with reduced mercury that pass the TCLP standards andthat are derivable from components that are readily commerciallyavailable.

An object of the present invention is to provide fluorescent lamps oflite-white color with reduced mercury consumption. (The term“lite-white” or “lite white” refers to a color of light from an energyconserving fluorescent lamp which has a high lumen output, typically anoutput higher than the output from a cool white color fluorescent lamp.)

Another object of the invention is to provide phosphor blends that areuseful in the manufacture of such fluorescent lamps of lite-white colorwith reduced mercury consumption.

Yet another object of the present invention is to provide alternate andimproved phosphor blends (compared to such blends derived from calciumyellow halophosphate) that provide lamps having improved performance atan acceptable cost, and that also provide fluorescent lamps with reducedmercury that pass the TCLP standards, all such phosphor blends and lampsderived therefrom being derived from components that are readilycommercially available.

These and other objects of the invention are accomplished by providingan electric lamp having an envelope with an inner surface and at leastone electrode, preferably electrodes located at both ends of theenvelope tube. The lamp may be a straight fluorescent tube, for exampleof the type as illustrated in the embodiment of the invention shown inFIG. 1 such as T12 straight Econowatt lamps, or it may be a lamp thatincludes an envelope of convoluted configuration to a desired shape suchas an envelope having at least two straight leg segments joined by aU-bent section as illustrated in the embodiment of the invention shownschematically in FIG. 2 or as in PL lamps, Circleline lamps, SLS lamps,etc. In either embodiment, the electrodes transfer electric power togenerate ultraviolet radiation in the envelope which is filled withmercury and a charge sustaining gas. Optionally, as in the case of thestraight envelope fluorescent lamps, the inner surface of the envelopemay be pre-coated with a metal oxide layer, such as an aluminum oxidelayer, to reflect ultraviolet radiation back into the envelope. Suchpre-coats are not customarily used in the case of lamps with convolutedenvelopes although a flexible pre-coat may be used in the case of SLSlamps as mentioned further hereinbelow. Optionally also, asemiconductive precoat of tin oxide can be applied between the envelopeand the precoat layer as a starting aid.

A phosphor layer is formed over the inner surface, pre-coated or not, toconvert the ultraviolet radiation to visible list. In conventionallamps, the phosphor layer for a conventional F34T12 straight Econowattfluorescent lamp is preferably a small particle-sized cool-white calciumhalophosphate phosphor formed from a coating which comprises calciumhalophosphate activated with manganese and antimony. Similarly thephosphor layer for a conventional U-bend fluorescent lamp of cool-whitecolor contains a small particle-sized two phosphor mix of about 50%large particle cool-white calcium halophosphate activated with antimonyand manganese, and about 50% fines (particles smaller than average in amixture of particles varying in size) of cool-white calciumhalophosphate activated with manganese and antimony. The fines arenormally used to achieve good adhesion particularly in the convoluted orbent areas between the glass layer or coatings thereon and the phosphorlayer.

We have previously discovered that the color obtained from theconventional large particle phosphor blend can be achieved by a phosphorderived from a mixture of fines of warm-white calcium halophosphatephosphor, small-particle blue-halo calcium halophosphate phosphor, andcalcium-yellow calcium halophosphate phosphor. It has been found furtherthat using this phosphor blend makes it possible to achieve goodadhesion in the manufacture of convoluted lamps of the U-bend type whileusing low mercury doses in the fluorescent lamp making itenvironmentally benign. Such phosphors form the subject of our priorapplication Ser. No. 10/259,713, referred to above.

According to the present invention, a novel lite-white fluorescent lampis provided having a phosphor that comprises a mixture of a cool-whitehalophosphate, a red-emitting YOX, a green-emitting LAP, and ablue-emitting BAM.

The components of the phosphor blend may be selected from componentsthat are well known in the art.

The cool-white halophosphate component may be, for example, a calciumfluorochlorophosphate (apatite) doped with antimony and manganese withan emission of a nominal color point of about 4100K, and having thegeneral formula Ca₅(PO₄)₃FCl:Sb,Mn; the red-emitting YOX component isfor example trivalent yttrium oxide activated with europium having thegeneral formula Y₂O₃:Eu; the green-emitting LAP component may be, forexample cerium, terbium lanthanum phosphate having the general formulaLaPO₄:Ce,Th; and the blue-emitting BAM component may be for exampledivalent europium-activated barium magnesium hexa-aluminate having thegeneral formula BaMgAl₁₁O₁₇:Eu.

In other phosphor blends within the scope of the invention, a CATcomponent, for example, cerium, terbium magnesium hexa-aluminate, havingthe general formula: (Ce,Tb)MgAl₁₁O₁₉ or a CBT component, for examplecerium, terbium, gadolinium pentaborate having the general formula (Ce,Gd) MgB₅O₁₀:Tb may be substituted for the green-emitting LAP component.Also, a SCA component, for example divalent europium-activatedchloro-strontium, calcium, barium phosphate having the general formula:(Sr,Ca,Ba)₅(PO₄)₃Cl:Eu, or a SCAP component, for example divalenteuropium activated strontium chlorophosphate (apatite) having thegeneral formula: Sr₅(PO₄)₃Cl:Eu may be substituted for the BAM componentdescribed above.

Exemplary lite-white phosphor blends are provided which may comprise:

-   -   (1) from about 85% to about 96%, preferably about 94%, of a        cool-white halophosphate phosphor component;    -   (2) from about 1.6% to about 5.8%, preferably about 2.3%, of        red-emitting YOX component;    -   (3) from about 1.7% to about 6.5%, preferably about 2.6%, of a        green-emitting LAP component; and    -   (4) from about 0.7% to about 2.7%, preferably about 1.1% of a        blue-emitting BAM component,        -   wherein the percentages are percentages by weight, and the            total percentage of the components is equal to 100%.

Such phosphor blends result in low-mercury consuming lamps. Such lampsare comparable to low mercury Philips Alto lamps and permit use ofreduced amounts of mercury when compared to commercially available lamps(other, than the Philips Alto lamps) produced with other phosphors inwhich more mercury is required. In addition, lamps derived from thenovel phosphor blends of this invention exhibit a higher color renderingindex (CRI) than conventional cool-white and lite-white lamps (at thelite-white color point). For example, lamps derived from a singlecomponent cool-white phosphor exhibited a CRI of 62; lamps derived froma lite-white formulation comprising calcium yellow and BAM exhibited aCRI of 51; and lamps derived from a novel lite-white phosphor blend ofthe invention had a CRI of 64. Moreover, lamps of the invention may beproduced using a reduced lamp powder weight and result in a higher lumenoutput when compared to lamps derived from a lite-white formulationcomprising calcium yellow and BAM.

Mercury consumption is determined by the quantity of mercury which isbound on lamp components during operation of the lamp and is thus nolonger available for operation of the lamp. In the present invention, itis possible to have reduced amounts of mercury doped in fluorescentlamps and preferably in cool-white U-bend fluorescent lamps, making suchlamps environmentally benign and TCLP compliant.

Lamps derived from such phosphors of the invention also exhibitexcellent long-life characteristics.

Thus the invention in preferred embodiments encompasses an electric lampwhich comprises:

a lamp envelope having an inner surface;

means within the lamp envelope for generating ultraviolet radiation; and

a layer of a luminescent material that includes a phosphor thatcomprises a mixture of a cool-white halophosphate, a red-emitting YOX, agreen-emitting LAP, and a blue-emitting BAM.

FIG. 1 is a perspective view of one embodiment of a fluorescent lampaccording to the invention, partly in cross-section, partly broken away;

FIG. 2 is a sectional view of a U-bend fluorescent lamp according to asecond embodiment of the invention.

The figures are diagrammatic and not to scale.

The invention will be better understood with reference to the details ofspecific embodiments that follow:

With reference to FIG. 1, there is illustrated a low pressure mercuryvapor fluorescent lamp 1 with an elongated, straight lamp vessel, orbulb, 3. The bulb is of a conventional soda-lime glass. The lampincludes an electrode mount structure 5 at each end which includes acoiled tungsten filament 6 supported on conductive feed-throughs 7 and 9which extend through a glass press seal 11 in a mount stem 10. The mountstem is of a conventional lead-containing glass. The stem 10 seals theenvelope in a gas tight manner. The leads 7, 9 are connected to thepin-shaped contacts 13 of their respective bases 12 fixed at oppositeends of the lamp.

Further and optionally, a semiconductive precoat layer can be usedbetween the inner surface 15 and the precoat 16. Optionally also, theinner surface 15 of the outer envelope 3 is provided with amercury-protective layer or undercoat 16. The layer 16 may be providedto reduce the rate of mercury depletion caused by reactions with theglass of the envelope. The layer 16 may be an oxide formed from thegroup consisting of magnesium, aluminum, titanium, zirconium and therare earths. As used herein, the term “rare earths” means the elementsscandium, yttrium, lanthanum and the lanthanides. Both coatings extendthe full length of the bulb, completely circumferentially around thebulb inner wall. The stems 10 are free of any of the above coatings. Aphosphor coating 17 is disposed over the overcoat layer 16.

The discharge-sustaining filling includes an inert gas such as argon, ora mixture of argon and other gases, at a low pressure in combinationwith a quantity of mercury to sustain an arc discharge during lampoperation.

According to a particular embodiment, the lamp shown in FIG. 1 is anF34T12 ECONOWATT lamp.

With reference to FIG. 2, there is illustrated a schematic sectionalview of a U-bent lamp unit 1A with an elongated lamp vessel, or bulb, 3Ahaving leg segments 4 and a U-shaped section 4A. The bulb is of aconventional soda-lime glass. The lamp includes an electrode mountstructure 5A ending in a mount stem 10A of a conventionallead-containing glass which seals the envelope in a gas tight manner.The lamp leads (not shown) are connected to the pin-shaped contacts 13Aof their respective bases fixed at opposite ends of the lamp.

According to a particular embodiment, the sectional view shown in FIG. 2is a segment of a T12TLU fluorescent lamp although it may also be a PL,Circleline, or SLS fluorescent lamp.

EXAMPLE

A F34T12 ECONOWATT lamp was manufactured according to the inventionemploying about 4.4 mg of mercury and a phosphor coating of a mixture ofabout 94 wt % of a cool-white halophosphate, about 2.3 wt % of ared-emitting YOX, about 2.6 wt % of a green-emitting LAP, and about 1.1wt % of a blue-emitting BAM.

The total amount of bound mercury in lamps derived from the abovephosphor blend will not exceed 1.24 mg after 2500 hours operating hours.Based on historical data in our laboratories, the lamps will meet therated life of 20,000 hours. In addition, the lamps pass the TCLP testand are considered non-hazardous and may be disposed in landfills.

It will be understood that the above discussion is intended to be merelyillustrative of the present invention and should not be construed aslimiting the appended claims to any particular embodiment or group ofembodiments. Thus, while the present invention has been described inparticular detail with reference to specific exemplary embodimentsthereof, it should also be appreciated that numerous modifications andchanges may be made thereto without departing from the broader andintended spirit and scope of the invention as set forth in the claimsthat follow. The specification and drawings are accordingly to beregarded in an illustrative manner and are not intended to limit thescope of the appended claims.

In interpreting the appended claims, it should be understood that:

(a) the words “comprises” and “comprising” do not exclude the presenceof other elements or acts not listed in a given claim;

(b) the word “a” or “an” preceding an element does not exclude thepresence of a plurality of such elements;

(c) any reference signs in the claims do not limit their scope; and

(d) several “means” may be represented by the same item or hardware orsoftware implemented structure or function.

1. An electric lamp which comprises: a lamp envelope having an innersurface; means within the lamp envelope for generating ultravioletradiation; and a layer of a luminescent material on said inner surfacecomprising a phosphor derived from a mixture of a cool-white calciumhalophosphate, a red-emitting yttrium oxide (YOX), a green-emittingcerium, terbium lanthanum phosphate (LAP), and a blue-emittingeuropium-activated barium magnesium hexa-aluminate (BAM).
 2. A lamp asclaimed in claim 1, wherein a cerium, terbium magnesium hexa-aluminate(CAT) component, or a cerium, terbium, gadolinium pentaborate (CBT)component is substituted for the green-emitting (LAP) component.
 3. Alamp as claimed in claim 1, wherein a divalent europium-activatedchloro-strontium, calcium, barium phosphate (SCA) component, or adivalent europium activated strontium chlorophosphate (apatite) (SCAP)component is substituted for the BAM component.
 4. A lamp as claimed inclaim 1, wherein said phosphor comprises from about 85 wt % to about 96wt % of a cool-white calcium halophosphate, from about 1.6 to about 5.8wt % of a red-emitting yttrium oxide (YOX), from about 1.7 to about 6.5wt % of a green-emitting cerium, terbium lanthanum phosphate (LAP), andfrom about 0.7 to about 2.7 wt % of a blue-emitting europium-activatedbarium magnesium hexa-aluminate (BAM).
 5. A low pressure low-mercuryconsumption mercury vapor fluorescent lamp, comprising: a. a tubular,light transmissive lamp envelope having opposing sealed ends, an innertubular surface and enclosing a discharge space between said sealed endswith a volume; b. a filling of elemental mercury and a rare gas; c. apair of discharge electrodes each arranged at a respective sealed end ofsaid lamp envelope; d. means for connecting said discharge electrodes toa source of electric potential outside of said lamp envelope, wherebyduring lamp operation a gas discharge is maintained between saiddischarge electrodes, which gas discharge emits ultraviolet radiation;e. optionally, a first, light transmissive and ultraviolet radiationreflecting layer disposed adjacent said inner surface of said lampenvelope, and f. a layer of a luminescent material comprising a phosphorderived from a mixture of a cool-white calcium halophosphate, ared-emitting yttrium oxide (YOX), a green-emitting cerium, terbiumlanthanum phosphate (LAP), and a blue-emitting europium-activated bariummagnesium hexa-aluminate (BAM).
 6. A lamp as claimed in claim 5, whereinsaid phosphor comprises from about 85 wt % to about 96 wt % of acool-white calcium halophosphate, from about 1.6 to about 5.8 wt % of ared-emitting yttrium oxide (YOX), from about 1.7 to about 6.5 wt % of agreen-emitting cerium, terbium lanthanum phosphate (LAP), and from about0.7 to about 2.7 wt % of a blue-emitting europium-activated bariummagnesium hexa-aluminate (BAM).
 7. A lamp as claimed in claim 6, whereina conductive semiconductor layer of tin oxide is applied as a startingaid between the inner surface and the precoat layer.
 8. A low-mercuryconsumption mercury vapor fluorescent lamp, comprising: a. a tubular,light transmissive lamp envelope having opposing sealed ends, an innertubular surface and enclosing a discharge space between said sealed endswith a volume; b. a filling of elemental mercury and a rare gas; c. apair of discharge electrodes each arranged at a respective sealed end ofsaid lamp envelope; d. means for connecting said discharge electrodes toa source of electric potential outside of said lamp envelope, wherebyduring lamp operation a gas discharge is maintained between saiddischarge electrodes, which gas discharge emits ultraviolet radiation;e. optionally, a first, light transmissive and ultraviolet radiationreflecting pre-coat layer disposed adjacent said inner surface of saidlamp envelope; f. optionally, a conductive semiconductor layer of tinoxide applied as a starting aid between the inner surface and theprecoat layer; and g. a layer of a luminescent material comprising aphosphor derived from a mixture comprising from about 85 wt % to about96 wt % of a cool-white calcium halophosphate, from about 1.6 to about5.8 wt % of a red-emitting yttrium oxide (YOX), from about 1.7 to about6.5 wt % of a green-emitting cerium, terbium lanthanum phosphate (LAP),and from about 0.7 to about 2.7 wt % of a blue-emittingeuropium-activated barium magnesium hexa-aluminate (BAM).
 9. A lamp asclaimed in claim 8, wherein said envelope is convoluted and is selectedfrom the group of envelopes comprising at least two leg segments joinedby a bent-U section, and envelopes bent to a desired shape.
 10. Aphosphor blend for low-mercury consumption fluorescent lamps whichcomprises a mixture of a cool-white calcium halophosphate, ared-emitting yttrium oxide (YOX), a green-emitting cerium, terbiumlanthanum phosphate (LAP), and a blue-emitting europium-activated bariummagnesium hexa-aluminate (BAM).
 11. A phosphor blend as claimed in claim10, wherein said phosphor comprises a mixture of from about 85 wt % toabout 96 wt % of a cool-white calcium halophosphate, from about 1.6 toabout 5.8 wt % of a red-emitting yttrium oxide (YOX), from about 1.7 toabout 6.5 wt % of a green-emitting cerium, terbium lanthanum phosphate(LAP), and from about 0.7 to about 2.7 wt % of a blue-emittingeuropium-activated barium magnesium hexa-aluminate (BAM).
 12. A phosphorblend as claimed in claim 11, wherein a cerium, terbium magnesiumhexa-aluminate (CAT) component or a cerium, terbium, gadoliniumpentaborate (CBT) component is substituted for the green-emitting (LAP)component.
 13. A phosphor blend as claimed in claim 11, wherein adivalent europium-activated chloro-strontium, calcium, barium phosphate(SCA) component, or a divalent europium activated strontiumchlorophosphate (apatite) (SCAP) component is substituted for the BAMcomponent.